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Novice needs help with three phase motor controller

Discussion in 'Sensors and Actuators' started by T&F, Dec 14, 2014.

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  1. T&F

    T&F

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    Dec 14, 2014
    Hi, I'm looking to set up an automatic dust collection system in a woodworking work shop. We have 4 machines that are ducted into the same dust extractor( though would like to add more quite soon) and i want to set up a system where, when each machine turns on and off it turns the dust collector on and off at the same time. In addition to this, each machine has a pneumatic blast gate to open and close the ducting ports to it. the pneumatic gates have 24v 2 way solenoid valves fitted, so one way would need to be triggered when each machine is turned n and the other when its switched off. The dust collector is 5hp 415ac, and all of the machines are 415v and between 5 and 25hp.

    Des any one have some thoughts on a good way to run this type of set up. i'm not entirely sure where to start researching and would be extremely grateful if someone could point me in the right direction.

    Many thanks!
     
  2. Gryd3

    Gryd3

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    Jun 25, 2014
    So.. I got a few questions to start off with on the dust collector itself.

    What is the size of the ducting run to the collector? What is the size of ducting run to the machines? (4" or 6")
    For multiple machines at the same time, it is advised to gradually increase the size of the duct as you add additional runs to it. This can be loosely calculated by taking the sum of the cross-sectional areas of the ducts that you wish to join. Once you have the sum, you work backwards to find the new diameter for the duct that the smaller duct should join to. Alternatively if only one machine will be on at a time, you can run the same size duct through the entire shop. (This is usually sized based on the largest machine).
    The reasoning for above is that when multiple blast-gates are open, the ducting needs to be large enough to be able to provide ample air-flow. If the ducting is too small, then when an additional machine is used, the air-flow drops on each machine due to the restriction imposed by the 'same-sized' ducting technique.
    The other mistake is running ducting that is too large... this may not make immediate sense, but you are dealing with 'air-flow' as a volume over a function of time. So a properly sized duct and a duct that is too large will give you the same air-flow, but the properly sized smaller duct will accomplish this with a higher velocity. The larger duct allows a greater amount of air to be moved at the same time, but the result is at a slower rate. This faster velocity is very important to prevent debris from building up in the collection system. Such a build-up can make a portion of your collection system useless, and also pose a safety/fire hazard. Don't get me wrong. This does NOT mean smaller duct is 'better'. It means that it should be sized based on the air-flow of the system.
    This also means that if your current setup is the 'gradual increasing duct size' technique, then leaving multiple machines shut off... or having the blast-gates close will decrease the volume of air travelling through the system.. and while this will not pose an issue for the individual machines currently in use, it will cause the air velocity to slow down in the larger ducting where multiple machines may come together.

    So... long story short, your solution should only be employed if only one (or two tops... depending on collection requirements) machines are running, and the ductwork throughout the shop is all the same size. This is common for smaller shops.
    If you have ductwork that grows to a greater diameter as more machines are added toward the collector, then is would be best to leave all is not most blast-gates open at all time, or installing a by-pass valve at the end of one of the longer runs. This bypass is usually weighted or spring loaded, and will open to allow additional air to enter to keep the air velocity higher in the larger ducting preventing debris build-up.

    Also, because of the machines in question, it would be best if you were to call in an electrician to wire the required relays for you.
     
  3. T&F

    T&F

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    Dec 14, 2014
    Hi, thanks so much for your detailed response. we have 8" ducting and 6" drop down to each machine and have the air flow and velocity to handle at least 2 machines at once though certainly don't have the capacity to have all ducts open at once. . I've researched ducting and extraction reasonably thoroughly and am aware of the pros, cons and limitations of our system. ( a lot of my info/ knowledge has come from Bill Pentz dust extraction knowledge base)

    The part I'm not entirely sure about, hence exploring this forum, is the electrical system to automate it all. We have an electrician who has set up the wiring for our machines( he's a friend of a friend, i did all of the cable runs and he did the connections to machines and installed a new fuse box) I inquired about how to set up this system but he's not too interested in getting involved as hes working for us very cheaply. He said if you organize all of it i will come and wire it up.

    I gather that we need some kind of multi way relay or contactor, i know others have set up systems like this with either a single or multiple current sensor to activate a contactor on the dust collector. It seems quite straight foward if it were just one machine to trigger a relay but i cant seem to find any info on how to set up multiple inputs to the relay. I did start to explore using an ubiquiti controller but it seems far more complex than is necessary for something like this.

    Any help would be amazing.
    Thanks!!
     
  4. Gryd3

    Gryd3

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    Jun 25, 2014
    Sounds like you're on the right track. Good to hear you did your research!
    As far as electrical is concerned, the signalling sounds easy enough to manage, but I don't have the experience with what type of modules the electrician may have available.
    For example, I am unsure if there is a pre-made dust-proof unit that will take care of signalling for the opening and closing of the blast gate. I would much rather you and your electrician use existing modules to control your equipment. Perhaps someone like @hevans1944 has some more detailed ideas on the modules needed.
    It does sound however that you will need two different control signals... a momentary 24V pulse to open/close the blast gate, and 'most-likely' a constant voltage to hold the contact on for the dust collector. I say most likely, but there is some abstract modules available for automation that I'm sure would allow both to be controlled with the same signal.
    I really do think that your friend of a friend electrician should sit down with you and talk about the setup. Ideally, he should be familiar with such modules.
    If the module approach fails, then building the circuit to control the blast gates and dust collector can be done. I can help draw something up in this regard... but again, I would much rather use modules already designed for this application.
     
  5. BobK

    BobK

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    Jan 5, 2010
    Or you could put back to back electrolytics to make a non-polarized cap.

    Bobs
     
  6. Gryd3

    Gryd3

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    Jun 25, 2014
    Lol.. please elaborate Bob.
    I'm not sure how this fits.
     
  7. BobK

    BobK

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    Jan 5, 2010
    You can make a non-polarized 100uF capacitor by connecting together the - leads of two 200uF capacitors and using the two + leads as the leads of your non-polarized capacitor. I know it is counter-intuitive, but it really does work.

    Bob
     
  8. Gryd3

    Gryd3

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    Jun 25, 2014
    I'm sure it does.. but how does that help the OP with switching on a dust collector, and toggling the output to control a dust collector blast gate? I think you got the wrong thread ;)
     
  9. BobK

    BobK

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    Jan 5, 2010
    Sorry, posted to wrong thread!

    Bob
     
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